Forensic verification utilizing halftone boundaries

ABSTRACT

A forensic verification system ( 700 ) extracts a print signature via print signature extractor  710  from the boundary of a halftone contained in an image. The system ( 700 ) compares the print signature to a reference signature stored in a registry via comparator  720  to determine differences between the print signature and the reference signature. The system  700  performs a forensic-level statistical image analysis via forensic analyzer  730  on the print signature and the reference signature based on the comparison to authenticate the printed media.

BACKGROUND

In environments where sensitive or confidential documents are handled,such as in financial institutions, it is often desirable to have theability to trace who printed a document as well as when and where it wasprinted. For example, it may be desirable to know if a check or otherfinancial instrument was printed from an authorized source (e.g.,printer, location, and so forth) as opposed to being a fraudulent copyof the respective instrument. Electronic means, such as bar coding, havebeen applied to documents in an attempt to authenticate the legitimacyof the documents. Bar coding, for example, can unacceptably alter theappearance of the documents by embedding superfluous information such asthe bar code image into the document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example system for performing forensicverification of printed documents utilizing halftone boundaries.

FIG. 2 illustrates an example of a forensic verification encoding systemfor generating reference signatures from halftone boundaries.

FIG. 3 illustrates an example set of symbols that represent stegatoneencoding that employ edge refinement techniques.

FIG. 4 illustrates an example set of symbols that represent stegatoneencoding that does not employ edge refinement techniques.

FIG. 5 illustrates an example of a forensic verification decoding systemfor analyzing reference signatures and print signatures utilizinghalftone boundaries.

FIG. 6 illustrates an example method for performing forensicverification of printed documents utilizing halftone boundaries.

FIG. 7 illustrates an example of a forensic analysis system.

FIG. 1 illustrates an example system 100 for performing forensicverification of print media utilizing halftone boundaries to generateand verify print signatures. The system 100 includes a forensic encodingsystem 110 (also referred to as the encoding system) that utilizeshalftone boundaries to encode forensic information. As shown, theforensic encoding system 110 receives a graphic image for encodingforensic information and payload. Output from the encoding system 110includes a secure hardcopy and registry and support data that areemployed by a forensic recovery and verification system 120 to performforensic verification of printed documents and to recover payload datathat had been previously encoded. As used herein, forensic analysis andverification provide the means to authenticate a printed document. Thisincludes the ability to prove statistically whether or not a documentwas printed from an authorized source or is an unauthorized copy.

As an example of analysis and verification, electronic tickets andvouchers may be distributed from a ticket agency having an agencyprinter generate the tickets for their respective customers. The ticketsprinted from the agency printer are considered authorized and valid uponredemption. If someone were to print additional originals (electroniccopies) or copy the ticket utilizing a scanner and subsequent printer,such printing would be unauthorized and fraudulent. The system 100provides encoding and decoding of covert information placed withinportions of printed documents to enable authentication. “Covert” impliesthat the authentication information is encoded as part of the printedimage and thus undetectable by the naked eye. As can be appreciated, theauthentication processes described herein can be applied to any type ofprinted document where it is desirable to verify that a given documentcorresponds to a unique physical instantiation. This functionality couldalso be used for applications that include but are not limited to caseswhere it is desirable to trace to the origins of the equipment,organization, or people, that generated the document (e.g., provewhether or not the document was generated by a particular printer, by anauthorized printer, or conversely whether document was printed/copiedfrom an unauthorized printing source).

The system 100 can also be employed to authenticate the association oftwo or more items, for example (e.g., a label or medallion with aserialized document on which the label/medallion is affixed). Since grayscale printing processes are inherently bi-tonal, halftoning processescan be utilized for continuous-tone graphics or images by producing thevisual illusion of continuous tone though the arrangement of black andwhite pixels. One type of halftoning can be based on a clustered-dottechnique, where gray levels are rendered with arrays of black and whiteclusters of pixels where the clusters are of varying size and shape. Astegatone is a halftone example that utilizes shifted dot clusters toencode information into a portion of the printed image.

As shown, the encoder 110 can embed a payload into a halftone of agraphic image. The payload represents the data to be embedded in thehalftone that can also be later employed as part of the forensicverification process (e.g., to locate a reference print signature in aregistry). The encoding process includes shifting of the dot clusterswithin the halftone to encode the payload within the halftone. Thehalftone can represent any portion of a printed document. For example,this could include a graphical feature such as a circle or square orirregular shaped image object or could include a symbol such as text ornumeric characters, for example. Although stegatones which include ahalftone pattern that holds steganographic information may be applied aspart of the encoding and decoding process of the system 100, any form ofhalftone (e.g., with or without addition of the payload) can be utilizedfor the boundary authentication processes described herein. In oneexample, halftones may not change from print-to-print and in otherexamples each version of a halftone in each single printed page can bedifferent. For instance, a halftone can be generated that varies onlywith the printing device, document author(s), user requesting the print,timestamp, security clearance, network state, or some combination ofthese and/or possibly other factors, for example.

The encoding system 110 creates and stores a reference signature in aregistry (described below with respect to FIG. 2) that acts as atraceable fingerprint for a printed document that enables detection ofauthorized or unauthorized printing. The reference signature can bederived from the boundary or exterior of a printed object or componentwithin the printed document. For example, if the symbol “a” were to havean encoded payload, the reference signature can be generated as afunction of the edges or outline of the symbol as opposed to theinterior halftones composing the symbol as will be illustrated belowwith respect to FIG. 3. In some examples, only the halftone may beemployed for the encoding and decoding processes described herein. Inother examples, a unique payload may be generated for the same commongraphic image and subsequently used to index the print signature in theregistry (e.g., one-to-one mapping between payload and printsignatures). In yet another case, the same payload may be applied to thegraphic image many times and used to index the resulting printsignatures in the registry (e.g., one-to-many mapping between payloadand print signatures).

To authenticate a printed document, a captured image to be analyzed isprocessed by the forensic recovery and verification system 120. Thecaptured image (e.g., snapshot image of printed document) should be ofsufficient resolution to enable the boundary analysis techniquesdescribed herein. For example, a high resolution camera or scanner(e.g., capable of acquiring an image at a resolution of 7200 dots perinch (DPI)) can be employed to capture printed media and generate theimage to be analyzed. The forensic recovery and verification system 120can generate a print signature that is derived from the boundary regionsof the recovered halftone (or stegatone if a payload was encoded for thereference signature). The print signature boundary analysis anddetection will be described below with respect to FIGS. 2-5. Theforensic recovery and verification system 120 compares the so recoveredprint signature to the reference print signature stored in the registry.

An authentication event occurs by the forensic recovery and verificationsystem 120 based on a comparison between the reference signature fromthe registry and the print signature derived from the captured image.This can include a statistical analysis (e.g., compare print signatureedge/boundary differences to a statistical threshold, where thethreshold is a designated level of statistical confidence to grantauthentication). The authentication can include other analysis such asan machine learning or artificial neural network analysis where trainedclassifiers analyze the respective print signatures in view of theretrieved reference signatures from the registry. It is noted that theforensic analysis and verification procedures described herein can beapplied to any type of printed document such as can be provided byprinters or other devices such as copiers, fax machines, andmulti-function print devices.

FIGS. 2-5 demonstrate some examples of forensic verification that can beimplemented utilizing print signature boundaries. Such description willbe provided in terms of specific examples such as the letter “a” as anexample halftone image; however, any portion or an image other thansymbols can be employed. Also, the examples include description ofstegatones which are a particular category of halftones. As notedpreviously, the halftone itself can be employed by the boundary andsignature analysis techniques described herein.

For purposes of simplification of explanation, in the present example,various components of the system 100, such as the encoding system 110and the forensic verification system 120, are illustrated and describedas performing different functions. However, one of ordinary skill in theart will understand and appreciate that the functions of the describedcomponents can be performed by different components, and thefunctionality of several components can be combined and executed on asingle component. The components can be implemented, for example, ascomputer executable instructions (e.g., software, firmware), hardware(e.g., a CPU, an application specific integrated circuit), or as acombination of both. In other examples, the components could bedistributed among remote devices across a network, for example. Theexecutable instructions 110 can be provided as a non-transitory computerreadable medium having the computer executable instructions storedthereon.

FIG. 2 illustrates an example of a forensic verification encoding system200 for generating reference print signatures from halftone boundaries.It is noted that FIG. 2 will also be described collectively with respectto FIGS. 3 and 4 which depict symbols that represent stegatone encodingsthat employ edge refinement techniques in the case of FIG. 3 and do notemploy edge refinement techniques in the case of FIG. 4. With respect toFIG. 2, a stegatone generator 210 receives a payload 212 and a graphicreference image 214 (also known as a mule image) and generates astegatone and the accompanying stegatone decode support data. Thereference image 214 is the portion of an image where data is encodedinto the respective halftone. A printer 220 prints the stegatone andgenerates a secure hardcopy which is photographed or imaged by capturedevice 230. A print signature profile extractor 240 processes thecaptured image of the secure hardcopy and deposits a reference printsignature in a print signature registry 250.

A print signature reference model generator 260 generates a referencemodel that is employed in the print signature extraction process. Asshown, stegatone decode and support data may be utilized by thereference model generator 260. Dashed lines 270 and 280 indicateadditional processing branches. For example, line 270 may include usingthe payload as an index in the print signature registry 250 tofacilitate future forensic verification (e.g., utilizing the indeximproves upon searching sequentially through the print signatureregistry for a matching print signature which can be both slower andless robust than using the index). As another example, the line 280demonstrates that the reference model generator 260 may also employ thestegatone to generate the reference model.

The system 200 provides a combination of a covert means of encoding datain hardcopy with halftones (e.g., steganographic halftones) and covertmeans of forensic verification with microscopic print signaturessurrounding the outside of a high contrast graphical image. Differentaspects include using a forensic reference model based on the inputimage, the edge-refined reference halftone, and/or the stegatone itself.

A function of the encoding system 200 is the creation of a securehardcopy document with an embedded payload 212 along with filing itsforensic fingerprint in the registry 250. The stegatone generator 210takes a data payload 212 and input image 214 referred to as a “mule”since it is the vehicle that transports the payload when printed. As anexample, one type of input images that can be utilized (others arepossible) includes the class of graphic grayscale images that are darkobjects surrounded by white space. Glyphs are members of this class andan example that is shown at 310 of FIG. 3, where the symbol “a” isdepicted. At 600 dpi, this lower case 20-point “a” would appear 3 mmtall but the example illustration at 310 shows it at much larger sizefor purposes of illustration. Stegatones can be generated by shiftingdot clusters within the halftone version of the reference image 214 toencode the payload 212 therein.

After preprocessing, a reference halftone as shown at 312 of FIG. 3 canbe generated from the mule image 214/310. The reference halftone can bea standard clustered-dot halftone, as shown at 312. Halftone cells canbe classified in a reference map such as 0-bit, 1-bit, 2-bit, or 3-bitdata carriers. Examples of these cells are depicted at 314 of FIG. 3. Inthis example, there are no 1-bit or 3-bit carrier cells. It is notedthat 0-bit carriers are referred to as reference cells since they areunchanged from the original cells and can be used for alignment. Forinstance, cells can be reference cells because they are too large to beshifted or too small to be detected. Cells can also be forced to bereference cells if their unaltered shape is desired to retain edgedetail or if they are needed to assist alignment. The payload 212 can beencoded by means of a single pixel shift of the halftone clusters, forexample. The data carrying capacity of the image of FIG. 3 is 234 bits,for example. A 234-bit payload can be encoded as the steganographichalftone or “stegatone” as shown at 320 of FIG. 3. Along with producingthis image, the stegatone generator 210 outputs stegatone decode supportdata that can be utilized for decoding the stegatone, possibleregeneration of the stegatone, and/or used to build a reference model inorder to support print signature extraction.

It is noted that many of the processes involved in the generation ofstegatones and in particular stegatone decode support data are commonacross all stegatones related to the same reference image and hence manyparts of this process may be performed once for the same stegatoneapplication. Moreover, the stegatone decode support data is generallyfixed and includes no information about the specific stegatone that hasbeen generated. In the most general case, during recovery of thestegatone data, no assumptions can be made a priori regarding thecontent of the specific stegatone.

Stegatone decode support data includes the mule image 214, referencehalftone, reference map, along with the shift and selection rules fordecoding and possibly auxiliary information related to any error-controlcoding applied to the stegatone payload. The stegatone is passed to theprinter 220 to create the printed hardcopy to secure by extracting andstoring its forensic print signature. Locating a forensic “finger print”of the hard copy is a task of the print signature profile extractor 240.The secure hardcopy is digitized via the capture device 230. The capturedevice 230 should be of sufficiently high resolution to render forensicquality detail. A captured hardcopy is shown at 324 of FIG. 3.

A reference model of the edge surrounding the graphic image is the idealagainst which the actual edge of the halftone is measured. Deriving thereference model is the task of the print signature reference modelgenerator 260. The print signature reference model generator 260 uses asinput the stegatone decode support data (e.g., provided by the stegatonegenerator 210 based on the payload and the mule image). When the muleimage 214 is used, a “standard” outline model can be generated. Forexample, the reference image of letter “a” 310 can be used directly togenerate a simple outline model. The image of 310 can be thresholdedinto a black and white image and connected components applied to theblack pixels to identify those pixels that belong to the character. Achain code can then be used to define the perimeter of the component inorder to define its outline model. Alternatively, similar processing canbe applied to examples of the reference image that have been printed ona suitable printer and captured at high resolution (e.g., forensicquality). These results can be combined to produce an averagecharacteristic print that is closer to physical reality.

An example of a standard model is depicted as an outline 328 of thecharacter “a” demonstrated at 330 of FIG. 3. Another more accurateoutline should more closely follow that of the halftone. For example,the stegatone generated in FIG. 3 employs an edge refinement process.This process retains a cleaner edge boundary surrounding the graphicobject. Halftone cells near the edge that would be carrier cells insteadretain the edge detail and become fixed reference cells. In this case,the edges of the reference halftone 312 can be used to generate thereference model for the resulting stegatones because those edges do notchange with the payload 212. An example of a resulting edge-refinedhalftone outline model is shown as the line 332 at example symbol 334 ofFIG. 3.

In both reference models shown at 330 and 334 of FIG. 3, the range(e.g., distance between outlines) over which the print signature isextracted is depicted by the distance between boundary lines 340 and350. The process for quantifying the print signature profile can includeextracting an image profile orthogonal to the outline model between theloci defined by these limits at a fixed number of points around theoutline model. This profile image can then be processed to recover adominant edge signal that represents the profile of the specific print.

The print signature can be normalized in part by defining it withrespect to the reference model, and can then be stored in the printsignature registry 250. The print signature can be reduced to a fewhundred bytes of data using the shape warp coding (SWC) The printsignature profile (which typically has 2000 or more elements) can bebroken into a fixed number of intervals (between 50 and 200 depending onthe desired balance between code length and statistical discrimination)over which variance is measured. Using the—mean such variance as a unitvalue, each interval can be quantized by rounding with respect to thisvalue. The difference between SWC's, termed the SDED or “shapedistortion encoding distance,” provides a discrimination metric that candistinguish veridical matches with the probability of falsepositives/negatives of less than one chance in a billion, for example.The SDED is a modified form of Hamming distance and is a sum of theabsolute differences in the respective elements of the SWC'srepresenting each signature profile.

FIG. 4 illustrates an example where edge refinement is not used. In thiscase, most of the halftone cells at the edges of the graphic object arecarrier cells and not reference cells. One of the reasons for not usingedge refinement is that the cells at the edges can be encoded to carrydata. Thus, the carrying capacity of the stegatone in FIG. 4 can beincreased relative to circumstances where edge refinement is used. Forexample, the carrying capacity for the character “a” can increase to 301bits from the 234 bits for where edge refinement is used in FIG. 3. Thedescription of the items in FIG. 4 is the same as those in FIG. 3 exceptat 410 of FIG. 4. In this example, the reference model can be generated(e.g., by reference model generator 260 of FIG. 2) based on thestegatone, shown at 420 of FIG. 4, and not from the reference halftoneas depicted at 430 of FIG. 4. This additional input is depicted in FIG.2 as the dashed line 280. While for the case of the mule reference imageand the reference halftone, the reference model can be generated byprinting and scanning example images of the actual halftone, while thismay not be possible for the case of the stegatone as the latter is notknown in advance of its generation. Hence, for some systems thestegatone reference model can only be generated from the digitalrepresentation of the stegatone. The process of generation may include amodel of the printing process in order to more accurately render asuitable outline model of the specific stegatone.

FIG. 5 illustrates an example of a forensic verification decoding system500 for analyzing reference signatures and print signatures fromhalftone boundaries. A secure hard copy print is imaged by a capturedevice 510. The captured image is sent to a print signature profileextractor 520. The print signature profile extractor 520 employs areference model to extract a print signature from the image of thesecure hardcopy. The print signature profile extractor 520 passes theextracted print signature to a forensic verification system 530 forforensic comparison with previously stored signatures from a printsignature registry 540. As part of the decoding process, a stegatonerecovery system 550 may process stegatone decode and support data, suchas disclosed above. The stegatone recovery system 550 can generatecorresponding payload data from the captured image and the support data.A print signature reference model generator 560 can generate thereference model for the profile extractor 520.

In other examples, the forensic verification decoding system 500 caninclude a stegatone generator 570 that can regenerate the stegatonebased on the payload and the stegatone decode and support data. Theregenerated stegatone can be utilized by the print signature referencemodel generator 560 in conjunction with the stegatone decode and supportdata, for example, to generate the reference model. Additionally oralternatively, the payload data extracted by the stegatone recoverysystem can also be passed (via dashed line 580) to the print signatureregistry 540 to provide an index to facilitate comparison of theextracted print signature with the previous registered version(s).

The system 500 recovers the payload from the stegatone (or utilizes thehalftone without payload) and verifies print signature with thesignatures stored in the registry 540. Given the secure hardcopydocument, hardware similar to what was used in the capture stage of theencode system of FIG. 2 can be used to create a digitized version of theprinted document. This is passed to the stegatone recovery system 550along with the stegatone decode support data as generated by theencoding system described above. One aspect to recovering the payload isthe precise alignment of the captured image. This exploits the fact thatthe boundaries of each halftone cell are known. For the purpose ofillustration, examples of the halftone cell boundaries are shownoverlaying the digital images at 312 and 320 of FIG. 3. Since thedigital stegatone will not yet be available, the reference halftone 312can be used to align the captured image, wherein the properly alignedcell boundary lines are also overlaid on this image such as shown at 324of FIG. 3. The cell shifts are subsequently located and the payload canbe recovered.

Because of imperfections in and/or noisy aspects of the print-captureprocess, it is possible for errors to be introduced into a payload. Forthis reason, error correction codes can be used. Aspects of theprocedure of interpreting the payload is analogous to the procedure ofreading digital information from other physical media, such as CDs, orsome types of disks since the processes that perform measurements todetermine the represented bits are typically not error-free, the datashould be protected with error correction codes. In the case ofstegatones, data can be represented by tiny shifts in sub-elements(e.g., a subset of pixels) of a printed dot cluster. Scratches or foldscan make interpretation of the shift ambiguous. Even without physicaldegradations of the document, nonlinearities in the printer or capturedevice can distort alignment which in turn can result in errors in datarecovery. Error correction coding utilizes redundancy in a strategicmanner to detect and correct such errors.

The print signature profile extractor 520 operates in a symmetricalmanner to that used in the encoder described in FIG. 2. As in theencoder, the reference model generator 560 only needs the mule inputimage if the standard model is used, or the reference halftone if thehalftone model is used, both of which are part of the stegatone decodesupport data set. When the stegatone model is needed, such as in theexample of 410 of FIG. 4, the stegatone generator 570 can regenerate thestegatone as illustrated as dashed lines in the example of FIG. 5. Whenthe payload is successfully recovered, the original digital stegatonecan be recreated based on the payload and the stegatone support data asmentioned above. Alternatively or additionally, the recovered payloadcan be used to address a subset of the registry 540 to speed the searchfor the correct print signature. When the reference model isestablished, such as by one or a combination of methods disclosedherein, the print signature profile can be extracted. The differencefrom the reference model is then used to compare with the printsignature registry 540 for forensic verification. One example includes acase where a different payload was used for each secure hardcopydocument. The recovered payload 580 could then address one printsignature in the registry to compare with the print signature extractedin 520. If the difference between the extracted and registeredsignatures was below a threshold then the authenticity of the securedocument can be verified.

In view of the foregoing structural and functional features describedabove, an example method will be better appreciated with reference toFIG. 6. While, for purposes of simplicity of explanation, the method isshown and described as executing serially, it is to be understood andappreciated that the method is not limited by the illustrated order, asparts of the method could occur in different orders and/or concurrentlyfrom that shown and described herein. Such a method can be executed by aprocessor and associated equipment, for example.

FIG. 6 illustrates an example method 600 for performing forensicverification of printed media utilizing halftone boundaries to generateand analyze print signatures. The method 600 includes recovering a printsignature from the boundary of a halftone contained in a captured imageat 610 (e.g., via pint signature extractor 710 of FIG. 7). At 620, themethod 600 includes comparing the print signature to a referencesignature to determine differences between the print signature and thereference signature (e.g., via comparator 720 of FIG. 7). At 630, themethod 600 includes performing a forensic analysis on the signaturesbased on the comparison to verify the image (e.g., via forensic analyzerof FIG. 7). Although not shown, in other examples, the method 600 caninclude encoding a payload into the halftone to form a stegatone. Thiscan include generating the stegatone with edge refinement that does notencode information in boundary cells of the stegatone. In anotherexample, the method 600 can include generating the stegatone withoutedge refinement that encodes payload information in boundary cells ofthe stegatone.

FIG. 7 illustrates an example of a forensic analysis system 700. Thesystem 700 includes computer executable instructions 708 that enable aforensic analysis and verification of printed documents. The system 700includes a print signature extractor 710 to extract a print signaturefrom a boundary of a halftone of an image of printed media. A comparator720 compares the print signature to a reference signature stored in aregistry to determine differences between the print signature and thereference signature. A forensic analyzer 730 performs a forensic-levelstatistical image analysis on the print signature and the referencesignature based on the comparison to authenticate the printed media.

What have been described above are examples. It is, of course, notpossible to describe every conceivable combination of components ormethodologies, but one of ordinary skill in the art will recognize thatmany further combinations and permutations are possible. Accordingly,the disclosure is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims. As used herein, the term“includes” means includes but not limited to, the term “including” meansincluding but not limited to. The term “based on” means based at leastin part on. Additionally, where the disclosure or claims recite “a,”“an,” “a first,” or “another” element, or the equivalent thereof, itshould be interpreted to include one or more than one such element,neither requiring nor excluding two or more such elements.

What is claimed is:
 1. A non-transitory computer readable medium comprising computer executable instructions that when executed cause a processor to: extract a boundary of a halftone of an image of printed media, wherein at least a portion of the boundary defines a print signature; and authenticate the printed media based on a forensic-level statistical image analysis, wherein the forensic-level statistical analysis comprises: accessing a reference signature stored in a registry, wherein the reference signature comprises payload information encoded into a boundary of a reference halftone; comparing the print signature to the reference signature to determine differences between the payload information of the reference signature and the print signature; and verifying whether the printed media is authentic based on the comparison.
 2. The non-transitory computer readable medium of claim 1, wherein the halftone of the reference signature is encoded with payload information to form a stegatone.
 3. A non-transitory computer readable medium comprising computer executable instructions that when executed cause a processor to: extract a print signature from a boundary of a halftone of an image of printed media; compare the print signature to a reference signature stored in a registry to determine differences between the print signature and the reference signature; and perform a forensic-level statistical image analysis on the print signature and the reference signature based on the comparison to authenticate the printed media, wherein the halftone is encoded with payload information, wherein the halftone is generated with a unique payload to form a one-to-one mapping between the print signature and the payload information.
 4. The non-transitory computer readable medium of claim 1, wherein the halftone of the reference signature is generated with a common payload to form a many-to-one mapping between the print signature and the payload information.
 5. A non-transitory computer readable medium comprising computer executable instructions that when executed cause a processor to: extract a print signature from a boundary of a halftone of an image of printed media; compare the print signature to a reference signature stored in a registry to determine differences between the print signature and the reference signature; and perform a forensic-level statistical image analysis on the print signature and the reference signature based on the comparison to authenticate the printed media wherein the halftone is encoded with payload information to form a stegatone that is generated with edge refinement that does not encode information in boundary cells of the stegatone.
 6. The non-transitory computer readable medium of claim 5, further comprising computer executable instructions that when executed cause the processor to generate a reference model to be employed in a recovery process for recovering the print signature.
 7. A non-transitory computer readable medium comprising computer executable instructions that when executed cause a processor to: extract a print signature from a boundary of a halftone of an image of printed media; compare the print signature to a reference signature stored in a registry to determine differences between the print signature and the reference signature; and perform a forensic-level statistical image analysis on the print signature and the reference signature based on the comparison to authenticate the printed media wherein the halftone is encoded with payload information to form a stegatone that is wherein the stegatone is generated without edge refinement that encodes the payload information in boundary cells of the stegatone.
 8. The non-transitory computer readable medium of claim 7, further comprising computer executable instructions that when executed cause the processor to generate a reference model to be employed in a recovery process for recovering the print signature.
 9. The non-transitory computer readable medium of claim 7, further comprising computer executable instructions that when executed cause the processor to perform shape warp coding to reduce the number of bytes in the print signature.
 10. A method, comprising: recovering a boundary of a halftone of a captured image of printed media, wherein at least a portion of the boundary defines a print signature; and authenticating the printed media based on a forensic-level statistical analysis, wherein the forensic-level statistic analysis comprises: accessing a reference signature stored in a registry, wherein the reference signature comprises payload information encoded into the boundary of a reference halftone; comparing the print signature to the reference signature to determine differences between the payload information of the reference signature and the print signature; and verifying whether the printed media is authentic based on the comparison.
 11. The method of claim 10, further comprising encoding payload information into the reference halftone to form a stegatone.
 12. The method of claim 11, further comprising generating the stegatone with edge refinement that does not encode the payload information in boundary cells of the stegatone.
 13. The method of claim 11, further comprising generating the stegatone without edge refinement that encodes the payload information in boundary cells of the stegatone.
 14. A system comprising: a memory for storing computer executable instructions; and a processing unit for accessing the memory and executing the computer executable instructions, the computer executable instructions comprising: a profile signature extractor to recover a boundary of halftone of an image of a captured image of printed media based on a reference model, wherein at least a portion of the boundary defines a print signature; a print signature reference model generator to provide the reference model for the profile signature extractor based on a stegatone; and a forensic verification system to authenticate the printed media by comparing the stegatone in the reference model to the print signature. 